First step to help would be change your username so you don't get reminded of how you feel every time you come on here.
Secondly, you are not pathetic and useless, there are people out there that love you and care about you and would hate to know you feel this way.
Thirdly, make a list of all the positive things about you and things you want to improve, then try to make those improvements.
Fourth...ly? Anyone who has caused you to feel this way, write their name or draw them on a piece of paper, imagine it's them and obliterate the paper to let out all your anger and hatred of them.
Fifth..ly? Any of those people on that list that you can contact, make sure they know how they made you feel as when they apologise if will feel like a weight lifted off your shoulders!
Sixth -ly the fact I spent 20 minutes of time I could be sleeping to write this to help you and I don't even know you just proves that anyone and everyone cares about you and you are loved and I am repeating an earlier point ok time to stop now.